EM schematic reading guide

Schematics

Every EM game included a schematic diagram when leaving the factory. Because EM games are now tens of years old, the diagrams are often lost or found their way into some repairmans collection. Many times can another games schematic diagram from the same timeframe be helpful, because there were much similarities between games. However, if you are troubleshooting a game specific feature, it would be nice to have a schematic available. But, it helps only if you know how to read it!

A repairman does not have to memorize every schematic. It is sufficient to know how to read them and recognize different parts and circuits. The information presented here lets you understand every schematic and make necessary adjustments and repairs in EM pinballs.

Drawing symbols

These are probably clear for everyone. Relay and solenoid coils do not differ in their drawing symbols. Sometimes the lamp symbol includes a little loop inside representing the filament.

Electronic hobbyists may wonder the switch symbol. It looks just like capacitor! Anyway these symbols are frequently used in relay diagrams not only in pinball schematics. A closing switch, that connects when actuated, is drawn as two parallel lines. An opening switch has a transverse line over the symbol. These can be connected to get a changeover switch or other multiple switches.

An important part in a pinball machine is the score motor. It has a large amount of switches in several different levels operated by motor cams. Motor operated switches are drawn with a circle around the switch symbol. Schematic diagrams are usually drawn with the motor at zero (home) position, and the switch symbol is marked with a letter for the level (height) and a number for the switch position. After 0 comes 1, and so on

Switches and coils

Score motor switches

Score motor switches are in multiple levels and positions. The level is marked by a letter and the position by a number.

Remember that the switches are drawn at the motor zero position. Then a switch closing at zero is drawn with an opening switches symbol because it is "normally" closed. Correspondingly switch closing at position 5 is drawn as closing switch, because it is "normally" open. "Normally" means here the motor being at zero position.

Examples

Color codes

Wire colors are marked in schematics with letters or numbers. Usually the wires have two colors, one for background, one for a stripe or dots. Those of us who memorize electronic components color codes, may be a little disappointed to notice the EM schematic color numbers are totally different! Fortunately different manufacturers used same numbers, and often the colors are marked in plain text.

Color	Abbreviation	Number
Red	R	1
Blue	Blu	2
Yellow	Y	3
Green	G	4
White	W	5
Brown	Br	6
Orange	O	7
Black	B	8
Gray	Gray	9
no stripe		0

The first number is the wires background color. The second number or letter is the color of stripes or dots. The codes are not always used, sometimes the color is in plain English.

Example:
Y = yellow wire
B-BLU = black wire with blue stripe
15 = red wire with white stripe

On old machines the wire colors might be faded. Especially red color has a tendency to fade to gray or even white! But when you open the wire bunch a bit, you can usually see the original color from an unfaded spot.

Real life fault and fixing

The bell rings when scoring ten points, but not with 100 points. Everything else seems to work. Schematic shows that the bell should ring both with 10 and with 100 points scoring:

Looking at the machine, it is found out that the 100 point score reel does work. This tells us that the 100 point relay is pulling. What is left to check, is the black/blue wire between bell and relay, and the relay switches.

Try connecting the bell solenoid black/blue wire with a test jumper lead to the yellow wire at 100 point relay switch. If the bell rings, problem must be with relay switch. If it doesn't ring there must be a cut wire between 100 point relay and the bell.